window.onscroll = function a() {
    var h = document.documentElement.scrollTop || document.body.scrollTop;
    var headerTop = document.getElementById('navbar');
    if (h > 100) {
        headerTop.style.background = '#0e031e';
    } else if (h <= 100) {
        headerTop.style.background = "rgba(0, 0, 0, 0)";
    }
}